1. Field of the Invention
The present invention relates to the preparation of powders of mixed, non-noble metal oxides, having high oxygen storage capacity, to be used, for example, in exhaust-purifying catalytic washcoats for internal combustion engines.
2. Description of the Related Art
Ceric oxide has been stabilized with other, non-noble metal oxides to be used as a catalyst and a catalyst support (washcoat). The washcoat generally is coated onto a base, often made of ceramic or metal, and a noble metal is deposited on the washcoat.
A typical application is catalytic converters for treating the exhaust gases produced by internal combustion engines. A noble metal catalyst, such as platinum, is deposited on the non-noble metal oxide washcoat and supported on framework within the converter. Catalytic conversion of the component by-products from the engine's exhaust gases are oxidized as the gases pass over the solid catalysts. See U.S. Pat. No. 3,993,572, to Hindin et al., for example.
Various factors influence catalytic activity. For example, the effectiveness of a solid catalyst generally increases with increased surface areas exposed to the material to be treated. Accordingly, maintaining particles of a solid catalyst in a highly divided state provides greater surface area, resulting in a more effective catalyst.
When a catalyst structure consists of a mixture of various catalytic components, such as ceria and zirconia, it follows that a more intimate mixture of the components will result in a more effective catalyst structure. The oxygen storage capacity of the washcoat in a catalytic converter is also of great importance, because the catalyst utilizes oxygen in order to oxidize components of the engine exhaust.
Various examples of catalyst structures are known. An alumina-based, catalyst carrier material formed by coprecipitation is disclosed in U.S. Pat. No. 4,331,565 to Schaefer et al. U.S. Pat. No. 4,940,685 to Sauvion et al. discloses a particulate, ceric oxide catalyst composition. The ceric oxide particulates are porous and have another metallic oxide dispersed therein. The composition is formed by coprecipitation, and does not provide the complete, solid solution of the present invention.
A composite powder, containing a catalytically-active noble metal and a promoter, is disclosed in U.S. Pat. No. 4,910,180 to Berndt et al. The agglomerated composite powder is formed by a spray pyrolysis process and subsequently is ball-milled to improve exposure of the noble metal.
The catalyst materials obtained by the known processes do not provide a catalyst washcoat made up of a complete solid solution of oxides of non-noble metal oxides having high oxygen storage capacity as provided by the present invention.